Menus are an important element of a graphical user interface (GUI) and appear ubiquitously in WIMP (window, icon, menu, pointing device) interfaces. They provide users a convenient means of interaction with the system to select and perform various operations. As software systems become more complex, menus expand in size and thereby affect navigation performance. To make menu navigation more efficient and to categorize the selection process, menus are sometimes designed as cascading menus.
Although cascading menus provide the advantage of presenting a large number of selections within a small screen space, they are limited in several ways. In traditional cascading menus, selecting an item in the child submenu requires the user to move the cursor along an elongated path. As a result, menu navigation becomes more difficult with an increasing number of levels in submenus. Users have to slide their cursor through narrow paths causing them to make movement errors since longer and narrower paths decrease efficiency of steering with the mouse or a pointing device as described in the following references: Accot, J., Zhai, S., May 15-20, 1999. Performance evaluation of input devices in trajectory-based tasks: An application of the steering law. In: CHI '99: Proceedings of the SIGCHI Conference on Human Factors in Computing Systems. ACM Press, Pittsburgh, Pa., United States, pp. 466-472 and Tanvir, E., Cullen, J., Irani, P., Cockburn, A., 2008. AAMU: Adaptive activation area menus for improving selection in cascading pull-down menus. In: CHI '08: Proceeding of the twenty-sixth annual SIGCHI conference on Human factors in computing systems. ACM New York, N.Y. USA, 1381-1384. As shown in FIG. 1, an elongated and narrow path can cause unexpected selections and unintended submenu appearance or disappearance due to straying mouse movements.
Additionally, traditional cascading menus include a time delay. When users are navigating through a menu and bring their cursor to a cascading item, the child submenu is posted after a period of 200 ms. The time delay is intended to improve the steering problem but it slows down the navigation process. An alternate option is to click on the cascading item to open the child submenu to pre-empt the delay. This clicking further slows down the interaction process and over time it can become bothersome for the users. Also, the delay could be too long for some users and too short for others. Additionally, individual preferences depend on many factors, including expertise of the user, context of the operation they are performing, and user fatigue.
Researchers have developed theoretical models to predict performance in menu navigation and selection.
Fitts' law: Fitts' law is a robust and widely adopted model for human movement. It was first published by Paul Fitts in 1954 as Fitts. P., 1954. The information capacity of the human motor system in controlling the amplitude of movement. Journal of Experimental Psychology 47, 381-391. The law predicts the time required to move from a starting position to a final target area and describes the time as a function of the distance to the target and the size of the target. The mathematical model for Fitts' law and its applications to HCl was established by MacKenzie and is also known as the Shannon formulation. This is described in the following references: MacKenzie, I. S., 1992b. Movement time prediction in human-computer interfaces. In: Conference on Graphics Interface. Morgan Kaufmann Publishers Inc. Vancouver, British Columbia, Canada, pp. 140-150 and Pastel R., Apr. 24-27, 2006. Measuring the difficulty of steering through corners. In: CHI '06: Proceedings of the SIGCHI Conference on Human Factors in Computing Systems. ACM Press, Montreal, Quebec, Canada, pp. 1087-1096. The formulation quantifies the movement task's difficulty, known as the Index of Difficulty or ID, in terms of the distance required to capture the target and the size of the target.ID=log2(D/w+1),
where D is the distance and W is the width of the object (see [12] for details). The Movement Time or MT is described as:MT=a+b×ID,
where a and b are constants that are empirically determined by linear regression (see MacKenzie, I. S., 1992b. Movement time prediction in human-computer interfaces. In: Conference on Graphics Interface, Morgan Kaufmann Publishers Inc., Vancouver, British Columbia, Canada, pp. 140-150 for details). Fitts' law predicts that it is easier to capture a target with a large size and is closer to the cursor. This law has been used to model the action of pointing on computers using fingers and mice and has assisted in designing user interfaces. This is described in the following references: Ahlstrom, D., Apr. 2-7, 2005. Modeling and improving selection in cascading pull-down menus using Fitts' law the steering law and force fields. In: CHI '05: Proceedings of the SIGCHI Conference on Human Factors in Computing Systems. ACM Press, Portland, Oreg., USA pp. 61-70; Kobayashi, M., Igarashi, T., Nov. 2-5, 2003. Considering the direction of cursor movement for efficient traversal of cascading menus. In: UIST '03: Proceedings of the 16th Annual ACM Symposium on User Interface Software and Technology. ACM Press, Vancouver, Canada, pp. 91-94; and Tanvir, E., September 2009. Improving cascading menu selections with adaptive activation areas. Master's thesis University of Manitoba Department of Computer Science. For example, Fitts' law aided the design of pie menus and resulting studies have shown that pie menus are more efficient and more accurate in comparison to linear menu items as described in Callahan, J., Hopkins, D., Weiser, M., Shneiderman, B., Jun. 15-19, 1988. An empirical comparison of pie vs. linear menus. In: CHI '88: Proceedings of the SIGCHI Conference on Human Factors in Computing Systems. ACM Press, Washington D.C. United States, pp. 95-100. However, Fitts' law has its limitations as well. It applies only to movement in a single dimension and not to movement in two dimensions. Mackenzie and Buxton described in Sears, A., Shneiderman, B., 1994. Split menus: Effectively using selection frequency to organize menus. ACM Transactions on Computer-Human Inter-action (TOCHI) 1 (1), 27-51 some changes to improve the model's performance for 2D target acquisition tasks.
Steering Law: Accot's law or the steering law as described in Accot, J., Zhai, S., Apr. 18-23, 1997. Beyond Fitts' law: Models for trajectory based hci tasks. In: CHI '97: Proceedings of the SIGCHI Conference on Human Factors in Computing Systems. ACM Press, Atlanta, Ga., United States, pp. 295-302 is an extension of Fitts' law to two dimensional modeling and steering of human movement. It predicts the average time necessary to navigate or steer a pointing device (e.g., a mouse or stylus) through a 2D path, tunnel or trajectory. In this path, the user must travel from one end to the other as quickly as possible, while staying within the confines of the path. This law has been used in modeling users performance in navigating a hierarchical cascading menu and it is also used to evaluate the performance of various input devices as described in Accot, J., Zhai, S., May 15-20, 1999. Performance evaluation of input devices in trajectory-based tasks: An application of the steering law. In: CHI '99: Proceedings of the SIGCHI Conference on Human Factors in Computing Systems. ACM Press, Pittsburgh, Pa., United States, pp. 466-472. This model describes that the time required to travel a trajectory is directly proportional to the distance traveled and inversely proportional to the width of the path. The steering law was mathematically derived from Fitts' law. In its general form, the steering law expresses the time T required to steer through a tunnel as:T=a+b(A/W),
where T is the average time to navigate through the path. W is the width of the path. A is the length of the path and a and b are empirically-determined constants (see Accot, J., Zhai, S., May 15-20, 1999. Performance evaluation of input devices in trajectory-based tasks: An application of the steering law. In: CHI '99: Proceedings of the SIGCHI Conference on Human Factors in Computing Systems. ACM Press, Pittsburgh, Pa., United States, pp. 466-472 for details). A limitation of the steering law is that the law has been verified for only a few path shapes and widths. For instance, steering is difficult through sharp corners and narrow paths as described in Tanvir, E., Cullen, J., Irani, P., Cockburn, A., 2008. AAMU: Adaptive activation area menus for improving selection in cascading pull-down menus. In: CHI '08: Proceeding of the twenty-sixth annual SIGCHI conference on Human factors in computing systems. ACM, New York, N.Y., USA, pp. 1381-1384, which explains the navigation problems in traditional menus.
Menu Types
Software applications are becoming increasingly complex. More functionality is offered with every new version and, as a result. GUIs are also increasing in complexity. Menus are multiplying in size, making it more difficult for the user to navigate through them. There are various categories of menus for different device types and researchers have developed a number of menu designs for each category to improve menu navigation and the selection process in user interfaces. The main categories include:
Linear Cascading Menus: Linear menus are the most common type of menus in use. They can be used with mice or pens. Menu items are generally arranged in a linear format, listing items from the top to the bottom of the screen or window. The submenus are arranged hierarchically, i.e., a parent cascaded item contains the submenu. The linear cascading menus are further categorized as:
Pull-Down Menus: They are usually used in menu bars, which are located at the top of the window or screen. A user activates the menu by clicking on its name and the menu opens in a drop-down form, presenting the possible operations that could be performed. An example is the menu bar in Microsoft Word.
Pop-Up Menus: A pop-up menu, unlike the drop down menu, can open anywhere on the screen based on the cursor position. An example is the context menu in Microsoft Windows, which is activated by right clicking the mouse.
Pen-Based Menus: Pen-based systems allow users to interact using a stylus instead of a traditional keyboard and mouse. Marking menus as described in Mackenzie, I. S., 1992a. Fitts' law as a research and design tool in human-computer interaction. Human-Computer Interaction 7, 91-139 are an example of pen-based menus. A marking menu allows a user to perform a menu selection by either popping-up a radial (or pie) menu, or by making a straight mark in the direction of the desired menu item without popping-up the menu. Unlike linear menus, marking menus can be operated “eyes free” because selection is based on direction of movement, not position.
Adaptive Menus: Researchers have designed different menu organization schemes for pull-down menus to reduce Fitts' law targeting requirements and to improve performance. Adaptive menus, as the name suggests, dynamically change their appearance or content over time in response to how they are being used. For example, an item list in a menu could be restructured based on usage frequency. Frequently used items are dynamically arranged on the top. Users have no control over the restructuring process. An example of an adaptive menu is the menu bar in the Microsoft Office 2003 suite. Split menus are an example of adaptive menus.
Adaptable Menus: Adaptable menus are user controlled and allow the users to customize the interface on the basis of individual preferences. For example, users can choose the menu items they want to have displayed in the top partition, as well as modify the existing arrangement. A comparison of static, adaptive, and adaptable menus as described in. Findlater, L., McGrenere, J., Apr. 24-29, 2004. A comparison of static adaptive and adaptable menus. In: CHI '04: Proceedings of the SIGCHI Conference on Human Factors in Computing Systems. ACM Press, Vienna, Austria, pp. 89-96, showed that users could optimize their performance if they knew about the possibility of adapting and were able to adapt their menus with a simple interface. Additionally, the results suggested that providing users with control over their menus can lead to better perceived performance and higher overall satisfaction.
Improvements to Cascading Menus
Cascading menus are the most commonly-used technique for handling hierarchical menus, however, selecting items from cascading menus is prone to errors. Cascading menus demand a high level of steering accuracy as they require the users to navigate through elongated paths. Also, conventional cascading menus are implemented with an explicit delay for the posting and unposting of the child submenu. This delay makes the selection process very slow. With the increase in complexity and size of cascading menus, there is an increasing demand for improving their design in order to make the navigation and selection process faster and easier. Researchers have designed various techniques to resolve the problems of cascading pull-down menus. Performance improvements have been obtained by either decreasing the distance to the menu items, or by increasing the size of the menu item.
Techniques for Decreasing Distance
A simple solution to make menu selection and navigation process faster is by reducing the Fitts' Law targeting requirement, i.e., reducing the distance to the target. The steering law also predicts that movement time increases with the length of the path to be covered. Most of the above-mentioned techniques have only focused on the selection of first-level items in cascading pull-down menus. However, longer selection times are caused by steering through long distances, i.e., level two and above. The techniques in FIG. 2 have also been tested for higher cascading levels. Kobayashi and Igarashi as described in Kurtenbach, G., Buxton, W., Apr. 24-28, 1994. User teaming and performance with marking menus. In: CHI '94: Proceedings of the SIGCHI Conference on Human Factors in Computing Systems. ACM Press, Boston Mass., United States pp. 258-264 presented an improvement to increase the usability of cascading menus by reducing the navigation distance and avoiding the unintended menu posting/unposting. This technique has two components. The first considers the direction of the cursor movement to determine the menu behavior. Vertical movement of the cursor changes the highlighted item within the current menu and the horizontal motion opens and closes the child submenus, therefore, eliminating the unwanted submenu activation during menu navigation. Second, when the horizontal motion occurs, the submenu pops up near the cursor position, hence, reducing the length of the movement path, see FIG. 2. A user must move the cursor to the right to open up a submenu or to the left to close the submenu and return to the parent menu.
A user study as described in Kurtenbach, G., Buxton, W., Apr. 24-28, 1994. User learning and performance with marking menus. In: CHI '94: Proceedings of the SIGCHI Conference on Human Factors in Computing Systems. ACM Press, Boston, Mass., United States, pp. 258-264 was conducted to evaluate the performance benefits of direction-based menus over traditional cascading menus. Users were asked to perform a menu selection task. The menuselection process started with the click of the mouse on a certain item in the menu bar. It ended with the selection of a highlighted menu item. The hierarchical levels of the menus for the above task ranged from two to five. The results of the study showed a 12% decrease in menu selection times as well as 85% fewer unintended submenu activations with direction-based menus.
Although the user study showed that this technique helped in decreasing movement path length, selection time and unexpected submenu activations, there are still limitations. First, the technique adds additional movements to invoke/revoke submenus, which is inconvenient and slows down the interaction process. Every time users need to view a submenu, they have to change the direction of motion, causing them to experience fatigue. Second, as the child submenu opens closer to the cursor position, submenus overlap their parent menus, and hide the rest of the parent menu items. If the user wishes to select a parent menu item while a submenu is open, this overlapping forces the user to make a left horizontal movement to close the submenu first before interacting with the parent menu. To make the selection process faster in traditional cascading pulldown menus, Ahlstrom introduced force fields as described in Ahlstrom D., Apr. 2-7, 2005. Modeling and improving selection in cascading pull-down menus using Fitts' law, the steering law and force fields. In: CHI '05: Proceedings of the SIGCHI Conference on Human Factors in Computing Systems. ACM Press, Portland, Oreg., USA, pp. 61-70. Force-field menus partially take control of the cursor movement from the users. Two types of force fields are used. First, when moving from left to right within a cascading item, the cursor is pushed towards the child menu and moves faster, optimizing the navigation process. Second, while moving within a non-cascading item, the force fields keep the cursor in the middle of the item, preventing the cursor from falling outside the parent menu; see FIG. 3. The most important benefit of force-field menus is that they keep the visual structure of the interface and the interaction technique unchanged.
Ahlstrom conducted a user study to evaluate the performance of force enhanced menus over traditional cascading menus as described in Ahlstrom, D., Apr. 2-7, 2005. Modeling and improving selection in cascading pull-down menus using Fitts' law, the steering law and force fields. In: CHI '05: Proceedings of the SIGCHI Conference on Human Factors in Computing Systems. ACM Press, Portland, Oreg., USA, pp. 61-70. Users were asked to perform a menu navigation and selection task. The user started the task by clicking a menu and then following the highlighted items. Once the target item was located, selecting the item completed the task. The menu navigation time was recorded. The hierarchical levels of the menus for the above task ranged from two to three. The results showed that the force fields decreased selection times, on average, by 18% when a mouse, a track point, or touch pad was used as an input device. One disadvantage of this technique is that while moving backwards (from right to left), the users experience resistance due to the force fields acting from left to right. Also, some users do not prefer losing control of the cursor.
Techniques for Increasing Width
The steering law suggests a second solution for faster steering by increasing the width of the path. A wider path is easier to navigate and less prone to movement errors, causing fewer unintended menu postings and unpostings.
A technique developed by Cockburn and Gin as described in Cockburn, A., Gin, A., Jun. 7-9, 2006. Faster cascading menu selections with enlarged activation areas, In: GI '06: Proceedings of the 2006 Conference on Graphics Interface. Canadian Information Processing Society, Quebec, Canada, pp. 65-71 is called Enlarged activation-area menus or EMUs, see FIG. 4. EMUs improve navigation through cascading menus by increasing the activation area of the parent menu associated with each cascaded submenu, providing a wider path for steering. Also, this technique allows a faster selection process by eliminating the problem of time delays. The activation areas for each cascading item are increased by extending them up to the end of the menu or by including all the non-cascading items before the next cascading item.
Cockburn and Gin conducted a user study to compare the performance of EMUs against traditional cascading menus as described in Cockburn, A., Gin, A., Jun. 7-9, 2006. Faster cascading menu selections with enlarged activation areas. In: GI '06: Proceedings of the 2006 Conference on Graphics Interface, Canadian Information Processing Society Quebec Canada, pp. 65-71. Users were asked to follow a highlighted path and select the highlighted target. The hierarchy of the menus for the above task was limited to second level menus. The evaluation showed that EMUs allow cascaded items to be selected up to 29% faster than traditional menus.
The problem with this technique is that the activation area is enlarged depending on the density of the cascading items in the parent menu. As a result, in case of adjacent cascading items, the size of the activation area will be equal to that of the traditional cascading menu, offering no performance benefits. Also, users can be distracted when a child cascading menu appears while they are targeting a non-cascading item that lies within the enlarged activation area. Fitts' Law also predicts that target acquisition can be improved by increasing the size of the target. Fisheye menus as described in Bederson, B. B., Nov. 6-8, 2000. Fisheye menus. In: UIST '00: Proceedings of the 13th Annual ACM Symposium on User Interface Software and Technology. ACM Press, San Diego, Calif., United States, pp. 217-225 and bubble cursors as described in Kobayashi, M., Igarashi, T., Nov. 2-5, 2003. Considering the direction of cursor movement for efficient traversal of cascading menus. In: UIST '03: Proceedings of the 16th Annual ACM Symposium on User Interface Software and Technology. ACM Press Vancouver Canada, pp. 91-94 are examples of such techniques. Fisheye menus dynamically increase the size of the target as the cursor approaches it as described in Bederson, B. B., Nov. 6-8, 2000. Fisheye menus. In: UIST '00: Proceedings of the 13th Annual ACM Symposium on User Interface Software and Technology. ACM Press San Diego, Calif. United States, pp. 217-225. They allow many items to be listed on one screen and are a good solution for viewing on small devices like personal digital assistants (PDAs). However, the evaluation of fisheye menus 141 showed them to be slower than traditional cascading menus as described in Bederson, B. B., Nov. 6-8, 2000. Fisheye menus. In: UIST '00: Proceedings of the 13th Annual ACM Symposium on User Interface Software and Technology. ACM Press, San Diego Calif., United States, pp. 217-225. Bubble cursors as described in Kobayashi, M., Igarashi, T., Nov. 2-5, 2003. Considering the direction of cursor movement for efficient traversal of cascading menus. In: UIST '03: Proceedings of the 16th Annual ACM Symposium on User Interface Software and Technology. ACM Press, Vancouver, Canada, pp. 91-94 increase the size of the cursor's activation area at runtime until it encloses at least one target. Bubble cursors are efficient for abstract targeting tasks, such as in computer games where the large cursor area helps in quick capturing of a smaller and fast moving object. However, bubble cursor offers no benefits in discrete targeting tasks where the target item is static and the location is known. An example of such a task is menu selection using cascading pull-down menus.
A further improvement to the method of improving item selection in cascading drop-down menus is disclosed in the article AAMU: Adaptive Activation Area Menus for Improving Selection in Cascading Pull-Down Menus by Tanvir, E., Cullen, J., Irani, P., and Cockburn, A., and which was published in April 2008 in CHI '08: Proceeding of the twenty-sixth annual SIGCHI conference on Human factors in computing systems by ACM, New, N.Y., USA, pp. 1381-1384. In this article, a triangular activation area is described which spans between an apex at a first end at the parent menu object and a second end spanning the height of the associated submenu. The results indicate that user can efficiently perform menu selection when provided with a broader steering path between the parent menu object and a submenu object which is desired to be selected; however, in some instances user may become undesirably trapped within the activation area.